<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <title>Title</title>
    <style>
        .father {
            width: 100px;
            height: 100px;
            background-color: pink;

        }

        .son {
            width: 50px;
            height: 50px;
            background-color: blue;
            margin-top: 20px;
        }

        .box1 {
            width: 100px;
            height: 100px;
            background-color: pink;
            margin-bottom: 80px;
            border-radius: 10px 20px 40px;
        }

        .box1 + .box2 {
            width: 100px;
            height: 100px;
            margin-top: 90px;
            background-color: purple;
        }

        button {
            border: 0;
        }
    </style>
</head>
<body>
<!--<div class="father">-->
<!--    <div class="son">外边距塌陷</div>-->
<!--</div>-->
<div class="box1"></div>
<div class="box2"></div>
<button>hello</button>
</body>
</html>